Heretofore, most transistorized movements of the balance wheel type have included a pair of coils, one coil serving as a pick-up coil and the other coil serving as a drive coil. U.S. Pat. Nos. 2,986,683 and 3,168,690 to M. J. Lavet et al. are typical. In such movements, the pick-up coil is connected to the input circuit of a transistor while the drive coil is connected to the output circuit of the same transistor. A pair of magnets are mounted on a balance wheel structure in a manner to provide a magnetic field to which both the pick-up coil and the drive coil respond. In this connection, the magnets move with the balance wheel in an oscillatory back and forth motion to induce a voltage in a winding of the coil. The effect of this operation is that the transistor is switched on as it responds to the voltage induced in the winding and that voltage is amplified at the output of the transistor and impressed across the winding of the drive coil in synchronism with the voltage induced in the winding of the pick-up coil to add energy to the system. This action maintains a sweeping oscillatory movement of the balance wheel.
Analog type positive feedback systems functioning to replace energy removed from a movable balance wheel system tend to self-oscillate. In order to avoid the tendency of self-oscillation, the prior art circuits have been highly damped and the feedback has been closely controlled. Such damping and control necessitate specific and tight component values which normally cannot be placed on an integrated chip. Additionally, these known prior art feedback systems including feedback circuits are subject to temperature variations which tend to change threshold chracteristics, for example, of the applied voltage, as well as current and temperature parameters. Moreover, time constants must be carefully chosen in order to avoid an adverse effect on timekeeping.
The prior art also includes other types of circuits employing synchronized blocking oscillators or multi-vibrators for purposes of overcoming the aforementioned adverse effects. However, these circuits require components which are relatively large and not practicable in use in small scale integration. With regard to these circuits, it again is necessary to carefully choose circuit time constants so as not to influence, but rather to minimize their effect on timekeeping.
It is a primary aspect of the present invention to provide a system in which a single-coil balance wheel operation may be obtained using readily integratable components and standard integration techniques. The circuit of the present invention is comparatively immune to timekeeping variations due to temperature, current, and voltage variation. Further, there are no circuit time constraints which must be carefully controlled or chosen to avoid an influence upon timekeeping, and the required electronics of the circuit are contained completely on a single integrated chip. Finally, the circuit design is such that the balance wheel and the balance wheel alone regulates timekeeping.